Fertilizer Provides Three Major Nutrients

Sixteen nutrients are considered essential to plant growth and development.
Thirteen of these nutrients are furnished by the soil.

Under natural conditions, plant nutrition is not a problem (note the forests,
woods and plains). However, for a successful and productive vegetable garden,
some type of fertilizer usually must be added.

But what's in a fertilizer that makes it so important? And what do those
three numbers mean? The numbers stand for three major nutrients - nitrogen,
phosphorus and potassium, in that order. The numbers tell how much of each
nutrient is present as a percentage of the total weight of the fertilizer.

Thus, a 50-pound sack of 10-20-10 contains 5 pounds of nitrogen, 10 pounds
of phosphorus and 5 pounds of potassium, or their chemical equivalents.
That's only 20 pounds total - the rest of the fertilizer is simply an inert
carrier or filler, such as sand, perlite or rice hulls.

Nitrogen is necessary for all vegetative growth - roots, leaves, stems,
flowers and fruits. Among other functions, it is partially responsible for
the green color of chlorophyll, and it is essential to protein formation.
A nitrogen deficiency causes lower leaves to turn yellow.

Phosphorus is essential to cell division, root formation, flowering and
fruiting. It's also involved in the storage and transfer of energy vital
to all growth processes. Consequently, a phosphorus deficiency causes stunted
growth and poor flowering and fruiting.

The role of potassium is not well defined, but experience shows that plants
cannot grow properly without it. Potassium deficiency symptoms vary, but
stunted growth and dark or purple discoloration are common symptoms in many
plants.

Iron, another problem element in many areas, is essential to chlorophyll
formation and the growth process. New growth on plants with an iron deficiency
have yellow leaves with green veins.¶